One teacher called it “beyond stupid” and added: “It was absolutely ridiculous.

“I’ve never worked in such cold. I’m all for saving the planet but this was barbaric.

“Nobody could work properly and kids could not even grip a pen through their gloves.” The mum of a 12-year-old at Ansford Academy in Castle Cary, Somerset, said: “She was shaking when she came home. I was absolutely furious.”

A dad added: “Turning the heating off in December is just mental.

“I can’t believe the kids learnt anything. I’m very angry with the school.”

But Mr Benzie, 52, defended the “successful” experiment last Friday — locally the coldest day of the winter so far — and vowed to stage regular “eco-days” at the 640-pupil school.

He said: “We cut the heat to see if we can lower our carbon footprint. We let pupils wear as many jumpers as they liked.

“Everyone seemed happy enough although it did get pretty chilly. We sent letters to parents telling them of the plan.

“We had only one complaint and that was from a member of staff. But in the end they just got on with it.”

Mr Benzie said he hoped for another eco-day next term, adding: “I’d like it to be a regular event. We have too much heating — sometimes I have to turn it down as it can make students fall asleep.

“The idea was actually thought up by a small number of pupils from our student eco-group.”